Method for producing a pedot film

ABSTRACT

A method for producing a PEDOT film on a substrate comprising a substrate and at least one PEDOT layer on a surface of the substrate is disclosed. The method comprises applying a solution comprising an oxidant and a base inhibitor on a surface of the substrate; subjecting the oxidant-coated substrate to a polymerization step by exposing the surface(s) of the oxidant-coated substrate to EDOT monomer vapour at a polymerization temperature; and wherein, during the polymerization step, the temperature of the oxidant-coated substrate is kept at a controlled substrate temperature and wherein the controlled substrate temperature is 2-40° C. lower than the polymerization temperature. Further is disclosed a conducting PEDOT film, an electronic device comprising the conducting PEDOT film and different uses of the conducting PEDOT film.

TECHNICAL FIELD

The present disclosure relates to a method for producing a poly (3,4-ethylenedioxythiophene) (PEDOT) film. The present disclosure further relates to a conductive PEDOT film. The present disclosure further relates to an electronic device comprising the conductive PEDOT film and the use of the conducting PEDOT film as an antistatic coating or an electrode in/of an electronic device.

BACKGROUND

Conducting PEDOT films are used in different fields like antistatic coatings, perovskite solar cells, organic solar cells, dye-sensitized solar cells, electrochemical transducers, electrochromic devices, electroluminescent devices, thermoelectric devices, smart windows, OLED's, optoelectronics and supercapacitors. Conducting PEDOT films may be manufactured by e.g. electrochemical polymerization of PEDOT on conducting substrate, oxidative chemical vapor deposition (oCVD) or vacuum vapor phase polymerization (VVPP) technique. When forming a conductive PEDOT film for electronic devices, their conductivity, low sheet resistance, morphology (roughness average) and optical transparency is of importance.

SUMMARY

A method for producing a poly (3,4-ethylenedioxythiophene) (PEDOT) film on a substrate comprising a substrate and at least one PEDOT layer on at least one surface of the substrate is disclosed. The method may comprise: applying a solution comprising an oxidant and a base inhibitor on at least one surface of the substrate so as to form an oxidant coating on at least one surface of the substrate; subjecting the oxidant-coated substrate formed to a polymerization step by exposing the surface(s) of the oxidant-coated substrate to 3,4-ethylenedioxythiophene (EDOT) monomer vapour at a polymerization temperature to form a PEDOT layer on the surface(s) of the oxidant-coated substrate; and wherein, during the polymerization step, the temperature of the oxidant-coated substrate is kept at a controlled substrate temperature and wherein the controlled substrate temperature is 2-40° C. lower than the polymerization temperature.

Further, a conducting PEDOT film is disclosed. The conducting PEDOT film may comprise a non-conductive substrate; a PEDOT layer having anions from an oxidant/oxidants embedded in the PEDOT layer on the non-conductive substrate, wherein the conducting PEDOT film has conductivity of over 2100 S/cm and sheet resistance of below 200 Ω/□.

Further, a conducting PEDOT film which is obtainable by the method for producing a PEDOT film comprising a non-conductive substrate and at least one PEDOT layer on at least one surface of the non-conductive substrate as disclosed in the present disclosure is disclosed.

Further, an electronic device is disclosed. The electronic device may comprise the conducting PE-DOT film as disclosed in the present disclosure.

Further, uses of the conducting PEDOT film are disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the embodiments and constitute a part of this specification, illustrate various embodiments. In the drawings:

FIG. 1 illustrates the vapor phase polymerization cell for carrying out the vapour phase polymerization.

FIG. 2 illustrates the Raman Spectrum of 6 layer PEDOT film produced by the vapour phase polymerization method.

FIG. 3 illustrates AFM images of 1 L) 1 layer of PEDOT, 2 L) 2 layers of PEDOT, 3 L) 3 layers of PEDOT, 4 L) 4 layers of PEDOT, 5 L) 5 layers of PEDOT, 6 L) 6 layers of PEDOT and SEM images of 1 L, 3 L and 6 L PEDOT.

FIG. 4 illustrates Cyclic voltammograms of 1 L to 6 L PEDOT (in 0.1 M TBABF₄ in MeCN with 100 mV/s scan rate).

FIG. 5 illustrates Cyclic voltammograms of 1 L PEDOT on glass and ITO coated glass in 6 mM Ferrocene solution with 20 mV/s scan rate.

DETAILED DESCRIPTION

The present application relates to a method for producing a poly (3,4-ethylenedioxythiophene) (PE-DOT) film comprising a substrate and at least one PE-DOT layer on at least one surface of the substrate, wherein the method comprises the steps of:

a) applying a solution comprising an oxidant and a base inhibitor on at least one surface of the substrate so as to form an oxidant coating on at least one surface of the substrate,

b)subjecting the oxidant-coated substrate formed in step a) to a polymerization step by exposing the surface(s) of the oxidant-coated substrate to 3,4-ethylenedioxythiophene (EDOT) monomer vapour at a polymerization temperature to form a PEDOT layer on the surface(s) of the oxidant-coated substrate, and

wherein, during the polymerization step, the temperature of the oxidant-coated substrate is kept at a controlled substrate temperature and wherein the controlled substrate temperature is 2-40° C. lower than the polymerization temperature.

The expression that the PEDOT layer is “on” the surface of the substrate in the PEDOT film should be understood in this specification, unless otherwise stated, as meaning that the PEDOT layer is polymerized or formed to lie on or upon the substrate or is being at least partly embedded therein. The substrate may serve as a carrier or support structure for the PEDOT layer. The substrate can be changed and the material of the substrate can vary according to the application to which the PEDOT film is to be used.

The expression “film” should be understood in this specification, unless otherwise stated, as referring to a structure having its lateral dimensions substantially larger than its thickness. In that sense, a film may be considered as being a “thin” structure.

The polymerization temperature is the temperature of the monomer vapour during the polymerization step.

In one embodiment, the substrate is non-conducting substrate. The expression that the substrate is “non-conductive” should be understood in this specification, unless otherwise stated, as meaning that the substrate has a sheet resistance of 10 Mohms/square or higher.

The non-conducting substrate may be a substrate such as a glass, a polymer, paper, cellulose, textile, fabric, wood, leather, cotton, ceramic, composites such as cellulose-wood composites, fibreglass, teflon, rubber, quartz, paint, carbon material and/or con-conducting mineral. The non-conducting polymer substrate may be selected from the group consisting of plastic material selected from a group consisting of polyester, polyethylene terephthalate (PET), polycarbonates (PC), polyamide (PI), polyester sulfone (PES), polystyrene (PS), and amorphous polyester (A-PET or PET-G) and mixtures thereof. The non-conducting substrate may be a flexible non-conducting substrate. Flexible substrates can be used for production of flexible PEDOT films that can be bent and folded.

The oxidant is a substance that induces polymerization of monomers, and can act as a dopant after polymerization of a conductive polymer. The embedded anions may remain within the PEDOT structure to act as dopant ions. The conductivity of PEDOT polymer may be due to the delocalization of electrons or holes upon oxidation (doping). The oxidant may be selected from the group consisting of iron(III)p-toluenesulfonate, iron(III)chloride, p-toluenesulphonic acid, iodine, bromine, molybdophosphoric acid, ammonium persulfate, DL-tartaric acid, polyacrylic acid, copper chloride, ferric chloride, naphthalenesulfonic acid, camphorsulfonic acid, Iron(III)toluene sulfonate, Iron(III)-perchlorate, Cu(ClO₄)₂.6H₂O, cerium (IV) ammonium nitrate, cerium (IV) sulfate and any mixtures thereof.

Base inhibitors decrease the activity of the oxidant and lower the rate of polymerization. This may alter the conductivity of deposited polymer. The base inhibitor may be selected from the group consisting of amine-based compounds and nitrogen atom-containing saturated or unsaturated heterocyclic compounds such as a pyridine-based, imidazole-based, or pyrrole-based compounds, water vapor, glycerol, and glycol derivatives, and mixtures thereof.

The oxidant solution of the present invention comprises the oxidant, the base inhibitor and a solvent. The solvent may be selected from the group consisting of organic solvents such as n-butanol methyl alcohol, 2-butyl alcohol, ethyl cellosolve, ethyl alcohol, cyclohexane, ethyl acetate, toluene, acetonitrile and methyl ethyl ketone and mixtures thereof.

In one embodiment, the PEDOT layer is doped.

In one embodiment, the method is carried out by vapour phase polymerization.

Vapour phase polymerization is a polymerization technique where only the monomer is converted into vapour phase. The VPP method may involve coating the substrate with an oxidant and base inhibitor solution followed by drying to remove traces of solvent.

In one embodiment, the vapour phase polymerization is carried out in atmospheric pressure. The vapour phase polymerization carried out in atmospheric pressure is easy to control. It does not need of pressure control or sophisticated device or vacuum oven. The method may be used also for production of large area films.

The polymerization temperature influences the properties of resulting PEDOT film such as the rate of polymerization by controlling rate of volatilization of monomers and/or the mobility of a polymer chain. The decrease of the temperature increases the concentration of vapour molecules. The substrate temperature and the polymerization temperature control the rate of polymerization. The polymerization temperature and the substrate temperature influence the properties of the formed PEDOT film such as conductivity, transparency, a sheet resistance and morphology. The controlled substrate temperature is a factor in controlling the rate of polymerization which in turn controls the morphology of the PEDOT films. The controlled substrate temperature brings the uniform and homogeneous nature to the PEDOT films.

In one embodiment, the solution comprising an oxidant and a base inhibitor is applied on one surface of the substrate and the oxidant coated surface of the substrate is exposed to EDOT monomer vapour at a polymerization temperature to form one PEDOT layer on the surface of the oxidant-coated substrate, thus producing a one-layered PEDOT film.

The method for producing multilayer PEDOT film may be carried out by layer-by-layer vapour phase polymerization. The PEDOT films may be formed by depositing PEDOT layers with wash steps in between.

In one embodiment the method comprises steps of

c) applying the solution comprising the oxidant and the base inhibitor on at least one surface of the PEDOT layer formed in step b) so as to form an oxidant coating on the at least one surface of the PEDOT layer,

d) subjecting the oxidant-coated PEDOT layer formed in step c) to a polymerization step by exposing the surface(s) of the oxidant-coated PEDOT layer to 3,4-ethylenedioxythiophene (EDOT) monomer vapour at a polymerization temperature to form a subsequent PEDOT layer on the surface(s) of the oxidant-coated PEDOT layer,

wherein, during the polymerization step, the temperature of the oxidant-coated PEDOT film is kept at a controlled substrate temperature and wherein the controlled substrate temperature is 2-40° C. lower than the polymerization temperature.

In one embodiment, the temperature of the oxidant-coated substrate is kept at a controlled substrate temperature during the polymerization step, and the controlled substrate temperature is 2-30° C. lower than the polymerization temperature.

In one embodiment, the temperature of the oxidant-coated substrate is kept at a controlled substrate temperature during the polymerization step, and the controlled substrate temperature is 3-20° C. lower than the polymerization temperature.

In one embodiment, the temperature of the oxidant-coated substrate is kept at a controlled substrate temperature during the polymerization step, and the controlled substrate temperature is 3-15° C. lower than the polymerization temperature.

In one embodiment, the temperature of the oxidant-coated substrate is kept at a controlled substrate temperature during the polymerization step, and the controlled substrate temperature is 5-15° C. lower than the polymerization temperature.

In one embodiment, the temperature of the oxidant-coated substrate is kept at a controlled substrate temperature during the polymerization step, and the controlled substrate temperature is 8-12° C. lower than the polymerization temperature.

In one embodiment, the solution comprising an oxidant and a base inhibitor is applied on the surface of the one PEDOT layer formed in step b), the one-layered PEDOT film, and the oxidant coated surface of the PEDOT layer is exposed to EDOT monomer vapour at a polymerization temperature to form a second PEDOT layer on the surface of the oxidant-coated PEDOT layer, thus producing a two-layered PEDOT film.

In one embodiment, the method comprises repeating step c) and step d) at least once for producing multilayer PEDOT film.

During polymerization step the substrate temperature and the polymerization temperature are controlled separately. In one embodiment, the polymerization temperature is 55-95° C. and the controlled substrate temperature is 40-70° C. In one embodiment, the polymerization temperature is 60-85° C. and the controlled substrate temperature is 45-70° C. In one embodiment, the polymerization temperature is 65-80° C. and the controlled substrate temperature is 55-70° C., or the polymerization temperature is 67-77° C. and the controlled substrate temperature is 56-66° C., or the polymerization temperature is 72-77° C. and the controlled substrate temperature is 61-66° C. The vapour phase polymerization of the present invention has no need of high temperature.

In one embodiment, the temperature of the oxidant-coated substrate and/or the oxidant-coated PEDOT film is kept at the controlled substrate temperature substantially during the entire polymerization step.

In one embodiment, the polymerization step is subdivided into sequential processing periods to tune the rate of polymerization.

In one embodiment, the polymerization step comprises two sequential processing periods, the temperature of the oxidant-coated substrate and/or the oxidant-coated PEDOT film is kept at the controlled substrate temperature throughout one of the processing periods.

In one embodiment, the polymerization step comprises three sequential processing periods, wherein the temperature of the oxidant-coated substrate and/or the oxidant-coated PEDOT film is kept at the controlled substrate temperature throughout the middle processing period.

During the processing period when the substrate is not kept at the controlled substrate temperature, the substrate temperature may change towards the ambient temperature, i.e. the polymerization temperature. The substrate temperature will cool towards the polymerization temperature, if the substrate temperature is higher than the polymerization temperature, or the substrate temperature will warm up towards the polymerization temperature, if it is lower than the polymerization temperature in the beginning of such a processing period.

In one embodiment, the method of the present application comprises the step of cleaning the substrate before step a). In one embodiment, the substrate was cleaned by ultra-sonication with a solvent. The solvent may be selected from the group consisting of organic solvents such as acetone and EtOH, water and mixtures thereof. The cleaning step may be repeated with same or different solvents.

In one embodiment, the cleaned substrate is dipped in hot solution of H₂O:NH₄OH (25%) :H₂O₂ (30%) as 5:1:1 volume ratio to remove any organic impurities left behind on the surface which was then followed by oxygen plasma treatment.

In one embodiment, the oxidant solution is spin-coated on at least one surface of the substrate in step a). In one embodiment, the oxidant solution is spin-coated on at least one surface of the at least one surface of the PEDOT layer formed in step c). In one embodiment, the oxidant solution is spin coated on the substrate at 800-3500 rpm. In one embodiment, the oxidant solution is spin coated on the substrate for 5-30 s.

In one embodiment, the method comprises cleaning, drying and/or heating the oxidant-coated non-conductive substrate from step a) before step b). In one embodiment, the method comprises cleaning, drying and/or heating the PEDOT film from step c) before step d). In one embodiment, the oxidant-coated non-conductive substrate is heated at 80-100° C. In one embodiment, the PEDOT film from step c) is heated at 80-100° C.

In one embodiment, the method comprises the step of annealing the PEDOT film at a temperature 50-100° C. after polymerization. The PEDOT film can be annealed to avoid stress fracture of the film during the washing step. The annealed PEDOT film may be washed to remove unreacted oxidant, monomer and any other impurities because the unconsumed oxidant and monomer traces may decrease the conductance. In one embodiment, the annealed PEDOT film is washed by dip rinsing thoroughly in ethanol followed by MeCN. In one embodiment, the annealed PEDOT film is dried. In one embodiment, the annealed PEDOT film is dried under dry nitrogen gas stream.

In one embodiment, the method comprises the step of cleaning the PEDOT polymer film received from step b) before the step c). In one embodiment, the PEDOT polymer film is cleaned by annealing the PEDOT film at a temperature 50-100° C. after polymerization. In one embodiment, the annealed PEDOT film is washed by dip rinsing thoroughly in ethanol followed by MeCN. In one embodiment, the annealed PEDOT film is dried. In one embodiment, the annealed PEDOT film is dried under dry nitrogen gas stream.

The polymerization time may effect on the properties such as a sheet resistance and a roughness average of the formed PEDOT film.

In one embodiment, the duration of the polymerization step is 1-20 minutes. In one embodiment, the duration of the polymerization step is 1-10 minutes. In one embodiment, the duration of the polymerization step is 2-8 minutes. The polymerization step is fast.

In one embodiment, the duration of the processing period of the polymerization step, wherein the temperature of the oxidant-coated non-conductive substrate and/or the oxidant-coated PEDOT film is kept at a controlled substrate temperature is 20-80% of the duration of the polymerization step.

In one embodiment, the duration of the polymerization step processing period, wherein the temperature of the oxidant-coated non-conductive substrate and/or the oxidant-coated PEDOT film is kept at a controlled substrate temperature is 30-60% of the duration of the polymerization step. In one embodiment, the duration of the polymerization step processing period, wherein the temperature of the oxidant-coated non-conductive substrate and/or the oxidant-coated PEDOT film is kept at a controlled substrate temperature is 35-40% of the duration of the polymerization step.

In one embodiment, the non-conductive substrate is glass. In one embodiment, the non-conductive substrate is polyethylene terephthalate (PET).

In one embodiment, the oxidant is Iron(III) p-toluenesulfonate hexahydrate (FETOS) In one embodiment, the base inhibitor is pyridine.

In one embodiment, the oxidant solution comprises or consists of FETOS and pyridine in n-butanol.

In one embodiment, the oxidant solution comprises the oxidant at a proportion of 5%-50% by weight relative to the volume of the oxidant solution.

The present application further relates to a conducting PEDOT film, comprising a non-conductive substrate, a PEDOT layer having anions from an oxidant/oxidants embedded in the PEDOT layer on the non-conductive substrate, wherein the conducting PEDOT film has conductivity of over 2100 S/cm and sheet resistance of below 200 Ω/□.

The present application further relates to a conducting PEDOT film obtainable by the method of the present application comprising a non-conductive substrate, a PEDOT layer having anions from an oxidant/oxidants embedded in the PEDOT layer on the non-conductive substrate, wherein the conducting PEDOT film has conductivity of over 2100 S/cm and sheet resistance of below 200 Ω/□.

In one embodiment, the conducting PEDOT film has a conductivity of over 3200 S/cm and a sheet resistance below 21 Ω/□. In one embodiment, the conducting PEDOT film has a conductivity of over 3200 S/cm and a sheet resistance 12 Ω/□.

Van der Pauw method can be used to calculate sheet resistance (r_(sheet)) for PEDOT films. The specific resistance (r) of the film is obtained by multiplying sheet resistance with film thickness (d), equation (1):

r=r _(sheet) d   (1)

The conductivity (s) of the film is obtained according to equation (2)

s=1/r   (2)

CV and EIS techniques can be used for electrochemical characterization. The charge (Q) is calculated by integration of the cyclic voltammogram in the potential range −0.25 to 0.75 V in the Origin software which is further processed by using following equations to obtain capacitance values:

Areal capacitance, C _(A) =Q/(ΔV*A)   (3)

Volumetric Capacitance, C _(V) =Q/(ΔV*V)   (4)

Where, ‘ΔV’ is the potential window, ‘A’ is the area and ‘V’ is the volume of working electrode.

In one embodiment, the conducting PEDOT film comprises 1-20 PEDOT layers on the non-conductive substrate. In one embodiment, the conducting PEDOT film comprises 1-15 PEDOT layers on the non-conductive substrate. In one embodiment, the conducting PEDOT film comprises 1-10 PEDOT layers on the non-conductive substrate.

In one embodiment, the the roughness average of the conducting PEDOT film is below 3.5 nm.

Roughness average values of the PEDOT film are obtained from the AFM images by using WSXM software. The roughness average (R_(a)) is the mean of the difference, in absolute value, between the average height and the height of each single point of the sample. This number varies with the interval range. It shows how uniform or rough the PEDOT film is.

In one embodiment, the % transmittance of the conducting PEDOT film at 550 nm is over 30% T. In one embodiment, the the % transmittance of the conducting PEDOT film is over 80% T.

Agilent 8453 spectrometer can be used to record the UV-Vis spectra. The % Transmittance (% T) is calculated from the absorbance data by using following equation (5),

(%T)=(10{circumflex over ( )}(−Abs))*100   (5)

In one embodiment, the non-conductive substrate of the PEDOT film is glass. In one embodiment, the non-conductive substrate of the PEDOT film is polyethylene terephthalate (PET).

In one embodiment, the PEDOT layer has anions from Iron(III) p-toluenesulfonate hexahydrate (FETOS) embedded in the PEDOT layer on the non-conductive substrate.

The thickness of the conducting PEDOT film may be designed in accordance with the properties of the conducting PEDOT film, especially the conductivity, resistance, roughness average or transmittance thereof or combinations of the properties. In one embodiment, the thickness of the PEDOT film is 10-500 nm, or 10-300 nm, or 20-200.

The present application further relates to an electronic device comprising a conducting PEDOT film of the present application.

In one embodiment, the electronic device is a display, a. flat panel. display, an optoelectronic devise such as an organic light emitting diode OLED, an organic solar cell, a dye-sensitized solar cell, a perovskite solar cell, a smart window, a fuel cell, an organic electrochemical transistor, an electrochemical transducer, an electrochromic device, an electroluminescent device, a. electroluminescent display, an organic capacitor, a supercapacitor, a sensor, a biosensor, an energy harvesting device, antistatic material, a photovoltaic device, a storage device or a thermoelectric device. In one embodiment, the electronic device is an optoelectronic device. In one embodiment, the electronic device is a transparent electrode. In one embodiment, the electronic device is a supercapacitor.

The present application further relates to the use of the conducting PEDOT film of the present application as an antistatic coating or an electrode in/of an electronic device.

The method of the present application has the added utility of being simple, low cost and fast due to the atmospheric pressure controlled polymerization. Further, the method of the present application has the added utility of producing thin multilayered PEDOT films at nanometer scale. Further, the method can be used to a large surface area and is not limited to conducting substrates. The PEDOT films of the present application have the added utility of being very uniform and homogeneous as well as smooth and flexible. Further, the PEDOT films of the present application have the added utility of having high conductivity and transmittance.

EXAMPLES

Reference will now be made in detail to various embodiments, an example of which is illustrated in the accompanying drawings.

The description below discloses some embodiments in such a detail that a person skilled in the art is able to utilize the embodiments based on the disclosure. Not all steps or features of the embodiments are discussed in detail, as many of the steps or features will be obvious for the person skilled in the art based on this specification.

For reasons of simplicity, item numbers will be maintained in the following exemplary embodiments in the case of repeating components.

FIG. 1 illustrates a vapor phase polymerization cell for carrying out vapour phase polymerization. The polymerization cell 1 comprises a stand 3 for the substrate 4 and for the metal block 5. Thermostatic baths 7 are attached to the polymerization cell 1 to keep the temperature of the monomer vapour 6 at the polymerization temperature. The thermostatic bath 8 is attached to the metal block 5 to keep the temperature of the substrate 4 at the controlled substrate temperature. The polymerization cell 1 comprises a lead 2 which is used to close the polymerization cell 1.

Example 1 Preparation of the PEDOT Film

Glass slides (substrates) (37.5 mm×25 mm) were cleaned by ultra-sonication with acetone, water and EtOH, respectively in each for 5 min. The cleaned substrates were dipped in hot solution (80° C.) of H₂O:NH₄OH (25%):H₂O₂ (30%) as 5:1:1 volume ratio for 5 min to remove any organic impurities left behind on the surface which was then followed by oxygen plasma treatment for 5 min. 0.236 M FETOS solution containing 0.141 M pyridine was prepared in n-butanol (oxidant solution). 60 pl of oxidant solution was spin coated on the substrate at 1450 rpm for 20 s. The oxidant coated substrate was dried on a hot plate at 90° C. for s. The dried substrate was transferred to a preheated cell 1 containing EDOT monomer 6 at 75° C. in such a way that the coated surface faced down towards the vapors. Polymerization was carried out for 4 min in 3 different steps. The cell 1 was covered with a glass lid 2 during first 90 s. The cell 1 was thereafter uncovered and the substrate temperature was kept at 65° C. by a heated metal block 5 for the next 90 s. The metal block 5 was removed and the cell 1 was covered with a glass lid 2 for 60 s. Annealing of the film was done after polymerization on a hot plate at 90° C. for 90 s. After annealing, the film was let to cool to room temperature and dip rinsed thoroughly in ethanol followed by MeCN to remove unreacted oxidant, monomer and any other impurities. Washing was done to remove the unconsumed oxidant and monomer traces which may otherwise decrease the conductance. After washing, the film was dried under dry nitrogen gas stream. The procedure was repeated from the spin coating step to prepare 1 to 6 layers of PEDOT on the glass substrate (1 L to 6 L PEDOT). The temperature of the cell 1 and metal block 5 was controlled by thermostat baths 7, 5.

The sheet resistance values and surface morphology of the PEDOT films were monitored by changing the parameters for the VPP method. The remaining parameters of the method were kept constant while monitoring one particular parameter at a time. The polymerization was carried out by keeping the temperature in the cell 1, the polymerization temperature, at 55, 65, 75, 85° C. for monitoring the VPP cell temperature. Polymerization time of 2, 4, 6, and 8 min were used to prepare the PEDOT films. The substrate temperature was not controlled while monitoring the VPP cell temperature and the polymerization time. PEDOT films were prepared at different substrate temperatures from 45° C. to 75° C. The substrate temperature was changed by controlling the temperature of the metal block 5. The annealing of the PEDOT films was performed at 60, 70, 80, 90, 100, and 110° C.

Characterization

Renishaw Qontor inVia Raman microscope was used to record Raman spectra (785 nm excitation). Agilent 8453 (up to 1000 nm) and Cary 5E spectrophotometer (VARIAN) (up to 2400 nm) were used to record UV-Vis-NIR measurements (background correction was done using an uncoated microscope glass slide). Van der Pauw method was used to calculate sheet resistance (r_(sheet)) for 1 L to 6 L PEDOT. Resistance values were recorded as the average of three measurements using the 4-point probe (square shape with a side a=2.2 mm) and Keithley multimeter (Model 2000). The specific resistance (r) and conductivity (s) of the film was calculated from equations (1) and (2).

AFM measurements were carried out using Veeco diCaliber scanning probe microscope operated in a tapping mode at room temperature. All AFM images were recorded using Bruker TESP-MT probe (resonant freq. 320 kHz, spring const. 42 N/m, length 125 μm, width 30 μm, Cantilever spec: 0.01-0.025 Ωcm Antimony (n) doped Silicon, 4 μm thick, tip spec: 10-15 μm height, 8 nm radius). WSXM software was used to determine mean roughness (roughness average (R_(a))) values of PEDOT films.

CV and EIS techniques were used for electrochemical characterization. CV measurements were carried out in conventional 3 electrode configuration using 0.1M TBA-BF₄/MeCN. VPP prepared PEDOT films on glass slides covered with different number of PEDOT layers were used as working electrodes. The area of the working electrode was 1.13 cm². A Ag/AgCl wire and a platinum wire were used as reference and counter electrode, respectively. Ag/AgCl reference electrode was calibrated before and after every electrochemical measurement using ferrocene redox couple (E_(1/2) (Fe/Fe⁺)=0.47 V). Cyclic voltammograms were recorded using Metrohm Autolab PGSTAT 101 potentiostat in a potential range from −0.25 V to 0.75 V at a scan rate of 100 mV/s for 1 L to 6 L PEDOT. The charge (Q) is calculated by integration of the cyclic voltammogram in the potential range −0.25 to 0.75 V in the Origin software which is further processed by using equations (3) and (4) to obtain capacitance values.

Results

The effect of the substrate temperature on the sheet resistance and the roughness average of PEDOT films are shown in table 1.

TABLE 1 Polymerization (Cell) temperature Sheet resistance Roughness average (° C.) (Ω/□) (nm) 55 235.56 0.77 65 208.18 0.68 75 201.26 0.75 85 224.15 1.13

The effect of the polymerization temperature on the sheet resistance and the roughness average of PEDOT films are shown in table 2.

TABLE 2 Substrate temperature Sheet resistance Roughness average (° C.) (Ω/□) (nm) 45 208.82 1.02 55 206.21 1.07 65 197.08 0.93 75 208.35 0.82

The polymerization temperature is a factor influencing the properties of resulting PEDOT films such as the rate of polymerization by controlling rate of volatilization of monomers (reactant), the mobility of a polymer chain, conductivity, and morphology. The roughness average (R_(a)) of the PEDOT film increased with an increase in the VPP cell 1 temperature (Table 1). This increase in the roughness-average is due to the high concentration of vapor at elevated temperatures forcing the condensation of vapor at the surface of a substrate. PEDOT films prepared were very uniform and homogeneous.

The roughness-average of the PEDOT films decreased with an increase in the substrate temperature (Table 2). This phenomenon is due to the fast condensation of monomer vapor at a low temperature resulting in less homogeneous films. As the temperature is increased, the condensation rate is decreased resulting in more uniform film formation. The same behavior also explains the decrease in the sheet resistance of the PEDOT film with the increase in substrate temperature up to 65° C. The sheet resistance increased for films prepared at 75° C. which is due to less deposition of monomer vapor favored by the high substrate temperature.

The effect of polymerization time on the sheet resistance and roughness average of PEDOT films are shown in table 3.

TABLE 3 Sheet resistance Roughness average Time (min) (Ω/□) (nm) 2 208.45 1.01 4 201.61 1.09 6 210.68 0.78 8 235.56 1.11

PEDOT films were prepared at different polymerization times i.e. 2, 4, 6, and 8 min. The PEDOT film prepared during 6 min showed the lowest roughness-average value and the PEDOT film prepared at 4 min polymerization time showed the lowest sheet resistance (Table 3). The sheet resistance decreased after annealing. The film annealed at 60°, 70, 80, and 90° C. showed all similar sheet resistance. The decrease in sheet resistance in the range of 60° C. to 90° C. of annealing temperature ensures the curing and the completion of the polymerization process.

Characterization of Multilayer PEDOT Films

FIG. 2 illustrates the Raman Spectrum of 6 layer PEDOT film. The band at 577, 699, 989, 1095, 1255, 1367, 1415, and 1530 cm⁻¹ are assigned to oxyethylene ring deformation, symmetric C—S—C deformations, oxyethylene ring deformations, C—O—C deformations, C_(α)-C_(α′) inter-ring stretching, C_(β)-C_(β′) stretching, symmetric C_(α)=C_(β) (—O) stretching, and C_(α)=C_(β) stretching, respectively.

FIG. 3 illustrates AFM images of 1 L) 1 layer of PEDOT, 2 L) 2 layers of PEDOT, 3 L) 3 layers of PEDOT, 4 L) 4 layers of PEDOT, 5 L) 5 layers of PEDOT, 6 L) 6 layers of PEDOT and SEM images of 1 L, 3 L and 6 L PEDOT. FIG. 3 shows the AFM images of 1 L to 6 L PEDOT and SEM images of 1 L, 3 L and 6 L with very uniform, homogeneous, sheet like nature of the films. Materials to be used in optoelectronics need to have high surface smoothness. From the AFM images and roughness average values (Table 4), it can be observed that the roughness doesn't exceed 1 nm for 1 L PEDOT and 4 nm for 6 L. This indicates that there is a small increase in surface roughness but the uniform, homogeneous, sheet like nature was not affected with the increment of additional layers. Thickness measurements were verified with the average of multiple measurements across the large scan area of the PEDOT films. 1 L PEDOT shows conductivity of 2178 S/cm and 6 L PEDOT shows the maximum value of 3208 S/cm (Table 4). Vapor phase polymerized PEDOT films prepared using FETOS as oxidant form closely packed large conductive domains which increase the in-plane conductivity. Sheet resistance decreases from 194.56 Ω/□ for 1 L PEDOT to 20.55 Ω/□ for 6 L PEDOT (Table 4). 2 L PEDOT showed 57.7% decrease in the sheet resistance from 1 L PEDOT but almost the same conductivities due to the increase in thickness. 3 L PEDOT shows 35.4% decrease in sheet resistance from 2 L PEDOT with a small increase in conductivity. Decrease in the sheet resistance when going from 3 L to 6 L PEDOT is almost linear but 3 L and 4 L PEDOT show almost similar conductivity values. Decrease in sheet resistance and increase in conductance from 1 L PEDOT to 6 L PEDOT also indicate a fast charge transfer from layer to layer (Table 4). This is facilitated by the efficient delocalization of the polaron and polaron pairs or bipolaron on PEDOT chains over different layers. This extended conjugation allows faster charge/electron transfer across the film.

Table 4 shows number of layers (L), thickness (d), sheet resistance (r_(sheet)), conductivity (s), areal capacitance (C_(A)), volumetric capacitance (C_(V)), percent transmittance (% T), and roughness average (R_(a)) for VPP produced PEDOT 1-6-layered films.

TABLE 4 d r_(sheet) s C_(A) C_(v) % T (at R_(a) L (nm) (Ω/□) (S/cm) (mF/cm²) (F/cm³) 550 nm) (nm) 1 23.6 194.6 2178 1.60 679 88 0.7 2 57.1 82.3 2128 3.42 600 77 1.6 3 81.2 53.2 2317 5.20 641 66 1.9 4 108.7 39.6 2325 7.35 676 56 2.3 5 125.0 28.5 2811 9.29 744 43 3.2 6 151.7 20.6 3208 10.67 704 35 3.4

According to the polaron theory of conductivity, electron transfer occurs through the motion of polarons and bipolarons/polaron pairs along the polymer chain with a reorganization of double and single bonds. Increased doping level results in an increase in conductivity.

As can be seen from table 4, a single layer of PEDOT is highly transparent.

FIG. 4 illustrates Cyclic voltammograms of 1 L to 6 L PEDOT (0.1 M TBABF₄ in MeCN with 100 mV/s scan rate).

FIG. 5 illustrates Cyclic voltammograms of 1 L PEDOT on glass and ITO coated glass in 6 mM Ferrocene solution with 20 mV/s scan rate.

In FIG. 4, cyclic voltammograms of rectangular shapes indicate reversible and efficient charging-discharging processes. Table 4 shows that there is an increase in capacitance values with every layer of PEDOT film. A film of 6 layers showed 10.67 mF/cm² (areal capacitance) and 703.58 F/cm³ (volumetric capacitance) capacitance values. In FIG. 5, cyclic voltammogram of a single layer of PEDOT is compared to bare ITO coated glass in 6 mM ferrocene solution. From the difference in peak potentials PEDOT required 60 mV less than the ITO coated glass. Calculated charge values for 1 L PEDOT and ITO coated glass are 42.93 mC and 36.48 mC, respectively. This can be explained by the higher surface area of PEDOT in comparison to ITO coated glass. Overall the ferrocene response of 1 L PEDOT is superior over ITO coated glass.

The high transparency, surface area, conductivity, and a very low surface roughness of one- and multi-layer PEDOT film makes them usable in optoelectronic devices and an alternative to ITO coated materials.

It is obvious to a person skilled in the art that with the advancement of technology, the basic idea may be implemented in various ways. The embodiments are thus not limited to the examples described above; instead they may vary within the scope of the claims.

The embodiments described hereinbefore may be used in any combination with each other. Several of the embodiments may be combined together to form a further embodiment. A method, a conducting PEDOT film, an electronic device, or a use, disclosed herein, may comprise at least one of the embodiments described hereinbefore. It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages. It will further be understood that reference to ‘an’ item refers to one or more of those items. The term “comprising” is used in this specification to mean including the feature(s) or act(s) followed thereafter, without excluding the presence of one or more additional features or acts. 

1. A method for producing a poly (3,4-ethylenedioxythiophene) (PEDOT) film comprising a substrate and at least one PEDOT layer on at least one surface of the substrate wherein the method comprises the steps of: a) applying a solution comprising an oxidant and a base inhibitor on at least one surface of the substrate so as to form an oxidant coating on at least one surface of the substrate, b) subjecting the oxidant-coated substrate formed in step a) to a polymerization step by exposing the surface(s) of the oxidant-coated substrate to 3,4-ethylenedioxythiophene (EDOT) monomer vapour at a polymerization temperature to form a PEDOT layer on the surface(s) of the oxidant-coated substrate, and wherein, during the polymerization step, the temperature of the oxidant-coated substrate is kept at a controlled substrate temperature and wherein the controlled substrate temperature is 2-40° C. lower than the polymerization temperature.
 2. The method of claim 1, wherein the substrate is a non-conducting substrate.
 3. The method of claim 1, wherein the method comprises the steps of: c) applying the solution comprising the oxidant and the base inhibitor on at least one surface of the PEDOT layer formed in step b) so as to form an oxidant coating on the at least one surface of the PEDOT layer, d) subjecting the oxidant-coated PEDOT layer formed in step c) to a polymerization step by exposing the surface(s) of the oxidant-coated PEDOT layer to 3,4-ethylenedioxythiophene (EDOT) monomer vapour at a polymerization temperature to form a subsequent PEDOT layer on the surface(s) of the oxidant-coated PEDOT layer, wherein, during the polymerization step, the temperature of the oxidant-coated PEDOT film is kept at a controlled substrate temperature and wherein the controlled substrate temperature is 2-40° C. lower than the polymerization temperature.
 4. The method of claim 3, wherein the method comprises repeating step c) and step d) at least once.
 5. The method of claim 1, wherein the temperature of the oxidant-coated substrate is kept at a controlled substrate temperature during the polymerization step, and the controlled substrate temperature is 2-30° C., or 3-20° C., or 3-15° C., or 5-15° C., or 8-12° C. lower than the polymerization temperature.
 6. The method of claim 1, wherein the method is vapour phase polymerization (VPP).
 7. The method of claim 1, wherein the polymerization temperature is 55-95° C. and the controlled substrate temperature is 40-70° C., or 60-85° C. and the controlled substrate temperature is 45-70° C., or the polymerization temperature is 65-80° C. and the controlled substrate temperature is 55-70° C., or the polymerization temperature is 67-77° C. and the controlled substrate temperature is 56-66° C., or the polymerization temperature is 72-77° C. and the controlled substrate temperature is 61-66° C.
 8. The method of claim 1, wherein the temperature of the oxidant-coated substrate and/or the oxidant-coated PEDOT film is kept at the controlled substrate temperature substantially during the entire polymerization step.
 9. The method of claim 1, wherein the polymerization step comprises two sequential processing periods, the temperature of the oxidant-coated substrate and/or the oxidant-coated PEDOT film is kept at the controlled substrate temperature throughout one of the processing periods.
 10. The method of claim 1, wherein the polymerization step comprises three sequential processing periods, wherein the temperature of the oxidant-coated substrate and/or the oxidant-coated PEDOT film is kept at the controlled substrate temperature throughout the middle processing period.
 11. The method of claim 1, wherein the method comprises the step of cleaning the substrate before step a).
 12. The method of claim 1, wherein the solution comprising the oxidant and the base inhibitor is spin-coated on at least one surface of the substrate in step a) and/or on at least one surface of the PEDOT layer formed in step c).
 13. The method of any of claim 1, wherein the method comprises cleaning, drying and/or heating the oxidant-coated substrate before step b), and/or the PEDOT polymer film from step c) before step d).
 14. The method of claim 1, wherein the method comprises the step of annealing the PEDOT film at a temperature of 50-100° C. after polymerization and optionally washing and drying the annealed PEDOT film.
 15. The method of any of claim 2, wherein the method comprises the step of cleaning the PEDOT polymer film received from step b) before step c).
 16. The method of claim 1, wherein the duration of the polymerization step is 1-20 minutes, or 1-10 minutes, or 2-8 minutes.
 17. The method of claim 1, wherein the duration of the polymerization step processing period wherein the temperature of the oxidant-coated substrate and/or the oxidant-coated PEDOT film is kept at a controlled substrate temperature is 20-80%, or 30-60%, or 35-40% of the duration of the polymerization step.
 18. The method of claim 1, wherein the non-conductive substrate is glass or polyethylene terephthalate (PET).
 19. The method of claim 1, wherein the oxidant is Iron(III) p-toluenesulfonate hexahydrate (FETOS).
 20. The method of claim 1, wherein the base inhibitor is pyridine.
 21. A conducting PEDOT film, comprising: a non-conductive substrate, a PEDOT layer having anions from an oxidant/oxidants embedded in the PEDOT layer on the non-conductive substrate, wherein the conducting PEDOT film has a conductivity of over 2100 S/cm and a sheet resistance of below 200 Ω/□.
 22. A conducting PEDOT film obtainable by the method defined in claim 2 comprising: a non-conductive substrate, a PEDOT layer having anions from an oxidant/oxidants embedded in the PEDOT layer on the non-conductive substrate, wherein the conducting PEDOT film has a conductivity of over 2100 S/cm and a sheet resistance of below 200 Ω/□.
 23. The conducting PEDOT film of claim 21 comprising 1-20, or 1-15 PEDOT layers on the non-conductive substrate.
 24. The conducting PEDOT film of claim 21, wherein the roughness average of the conducting PEDOT film is below 3.5 nm.
 25. The conducting PEDOT film of claim 21, wherein the % transmittance of the conducting PEDOT film is over 30% T.
 26. The conducting PEDOT film of claim 21, wherein the non-conductive substrate is glass or polyethylene terephthalate (PET).
 27. The conducting PEDOT film of claim 21, wherein the PEDOT layer has anions from Iron(III) p-toluenesulfonate hexahydrate (FETOS) embedded in the PEDOT layer on the non-conductive substrate.
 28. The conducting PEDOT film of claim 21, wherein the thickness of the film is 10-500 nm or 10 -200 nm.
 29. An electronic device, characterized in that the device comprises a conducting PEDOT film as defined in claim
 21. 30. An electronic device of claim 29, wherein the device is a display, a flat panel display, an optoelectronic devise such as an organic light emitting diode OLED, an organic solar cell, a dye-sensitized solar cell, a perovskite solar cell, a smart window, a fuel cell, an organic electrochemical transistor. an electrochemical transducer, an electrochromic device, an electroluminescent device, an electroluminescent display, an organic capacitor, a supercapacitor, a sensor, a biosensor, an energy harvesting device, an antistatic material, a photovoltaic device, a storage device or a thermoelectric device.
 31. Use of the conducting PEDOT film as defined in claim 21 as an antistatic coating or an electrode in/of an electronic device 